Field of the Invention:
The invention relates to a method for the positionally accurate adjustment and fixing of a microoptical element on a carrier by means of a device for the positionally accurate adjustment and fixing, having a heating device constructed as a radiant heater for supplying thermal radiation to fasten the microchip on the carrier by heating and soldering. This thermal radiation is guided through an imaging optical system onto the microchip. The device has an optical monitoring system which is assigned to the same imaging optical system.
The term microchip is to be understood broadly. For example, microchip includes semiconductor diodes and microlenses that are intended to be mounted with high accuracy on a carrier, also termed a xe2x80x9csubmountxe2x80x9d.
Known methods of the type mentioned at the beginning are distinguished in that the microchip is picked up by a suction nozzle or pincers and brought into the desired position with the aid of micromanipulators. The position is adjusted exactly with the aid of an image recognition system that usually has a camera with a tube and an imaging optical system. The image recognition system is located axially above the mounting position. The microchip is then lowered onto the appropriate carrier. The microchip and carrier are soldered or bonded to one another by heating. Resistance heating, gas heating, and radiant heating are alternate means for heating. The problem with the above-described device is that it requires a multiplicity of subcomponents for the heating source and the axial position monitor must be mounted in the relatively constricted space next to one another spatially in a unit. Another problem is that the thermal energy is not always delivered to the correct position.
Design Engineering, June, 1987, London, page 25 xe2x80x9cSensor Based Laser Scanner Links. . . xe2x80x9dteaches to use a laser as a radiant heater to fix a microchip onto a carrier and to guide the thermal radiation through the imaging optical system of an optical position monitor.
Both the camera and the exit optics of the laser beam from a fiber cable are arranged at the side next to the optical path of the imaging optical system. In this system, the optical radiation of the position monitor and the thermal radiation of the laser must be reflected into the beam path of the imaging optical system via inclined semitransparent mirrors. A detector for infrared light is arranged directly in the beam path of the imaging optical system. The detector studies characteristic radiation curves on the IR radiation, which allows the quality of the solder joints to be monitored. The IR radiation passes from the imaging optical system through the two semitransparent mirrors into the IR detector. The thermal radiation is thus first directed from the laser, via a beam splitter onto the component, and reflected from there. Only the reflected thermal radiation passes, as governed by the system, through the beam splitter of the laser and the beam splitter of the monitoring camera to the IR detector.
This arrangement has the disadvantage that readjustment of the thermal radiation cannot be performed until solder joints have actually been produced and analyzed. In the case of wrongly adjusted thermal radiation, the system cannot react before faulty soldering joints have been formed. This results in waste.
Instruments And Experimental Techniques, vol. 30, No. 6, part 2, November, 1987, pages 1494 to 1495 teaches not to fit an IR detector in the case of an arrangement of the generic type, but rather to fit a viewing optical system via which an operator can view the solder junction. A rotating mirror allows light to enter from the imaging optical system. An optical filter is situated in the path of the reflected thermal radiation upstream from the viewing optical system and the input of a monitoring camera.
Similar devices of the type described above are also known from EP 0 326 020 A and EP 0 491 192 A.
The object of the invention is to specify a method that makes particularly accurate positioning, adjustment, and fixing of the microoptical element on the carrier possible using the device described in the Field of the Invention.
According to the invention, the object is achieved by the features of patent claim 1.
The essential advantage of the invention is that the thermal energy for soldering or bonding the microchip can be introduced directly to the microchip itself. The same imaging optical system can be used to observe the microchip and to control the adjusted position by means of the optical monitoring device. This configuration creates a coaxial optical output coupling for simultaneous adjustment and fixing.
The optical position monitor can be arranged on an optical axis of the imaging optical system. The thermal radiation and radiation that can be detected for the optical position monitor are supplied laterally and reflected onto the optical axis of the imaging optical system with the aid of optical elements. Mirrors or beam splitters accomplish this. Monitoring systems for monitoring and controlling the radiant power can be arranged downstream of the beam splitters. Photodiodes can be used for this purpose. The beam splitters are configured in this case such that more than ninety percent (90%) of the radiant power is directed toward the imaging optical system and only a small remainder impinges on the photodiode.
The optical position monitor has a camera, a tubular body, and an imaging optical system. The camera preferably can be arranged on the optical axis of the imaging optical system. A filter can be placed upstream of the camera. In particular, the filter can be a cut-off filter that is transparent only to the light of the optical position monitor, that is to say the visible light or infrared light, and is opaque to the wavelength of the thermal radiation. This measure effectively protects the camera from the thermal radiation of the heating device.
A laser can generate the thermal radiation. Lasers can produce the very high energy density that is required.
Particularly suitable here are NdYag lasers or a bundle-fiber high-power semiconductor laser system. A xenon vapor lamp or the like also can be used in some circumstances.
An optical conductor should be provided for supplying the thermal radiation to the device. When the light is irradiated into the tube by means of an optical conductor such as a fiber or a fiber bundle, the tube design can be very small.
In another development of the device, an optical system is provided for parallelizing and controlling the focus of the thermal radiation so that the focal positions for the thermal radiation and the monitoring radiation can be brought into conformity with each other. This optical system serves, furthermore, initially to xe2x80x9cparallelizexe2x80x9d the thermal radiation.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in method for the positionally accurate adjustment and fixing of a microoptical element, the invention is nevertheless not intended to be limited to the details shown. Various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.